Fiber optic cables are cables that include one or more optical fibers that are used as a medium for transmitting optical communications signals. Fiber optic cables are used in a wide variety of applications such as, for example, in cable television networks, local area networks, vehicles, ships, airplanes, wide area networks and datacenters. Fiber optic cables may support very high data rate communications.
FIG. 1A is a perspective view of a conventional fiber optic cable 10. FIG. 1B is a cross-sectional view of one of the optical fibers 22 included in the fiber optic cable 10 of FIG. 1A. As shown in FIG. 1A, the fiber optic cable 10 includes an optical fiber bundle 20 that includes a plurality of optical fibers 22, a strength member 30 that may comprise, for example, a plurality of strength yarns 32 and an outer jacket 40. As shown in FIG. 1B, the optical fiber 22 includes a central core 24, a cladding layer 26 and a buffer coating 28. Typically, the coating 28 comprises an ultra-violet light cured urethane acrylate coating, although other coatings may be used. The core 24 and the cladding 26 may each be made of transparent glass (silica), although plastic is sometimes used. The cladding 26 has a lower index of refraction than the core 24. The difference in indexes of refraction of the core 24 and cladding 26 along with the angle at which an optical signal is injected into the core 24 may be selected so that the core 24 will act like a waveguide through which the optical signal will propagate with very low loss, reflecting off the surrounding cladding 26. The buffer coating 28 protects the core 24 and cladding 26 from moisture and/or physical damage.
Referring again to FIG. 1A, the strength yarns 32 may comprise, for example, aramid yarns or glass yarns. These strength yarns 32 further protect the optical fibers 22 from physical damage. The jacket 40 may comprise, for example, a polyvinyl chloride jacket that provides an additional layer of protection and holds all of the components of the cable 10 together to form an integral unit.
Each optical fiber 22 of fiber optic cable 10 may be physically spliced to an optical fiber of another cable or to network equipment via mechanical splicing or heat fusing. More commonly, however, a fiber optic cable, such as cable 10, will be terminated with one or more fiber optic connectors (not shown) to provide a fiber optic patch cord or jumper cable. The fiber optic connector may be used to connect the fiber optic cable to another fiber optic cable or to network equipment. When fiber optic cables include a plurality of optical fibers, one or both ends of the fiber optic cable may be broken out into subunits (i.e., smaller cable sections that each include a subset of the optical fibers) that are individually connectorized. Alternatively, fiber array connectors may be used to connectorize such multi-fiber fiber optic cables. Typically, these fiber array connectors align the optical fibers in a side-by-side configuration (or stacked layers of side-by-side optical fibers) for mating with similarly aligned optical fibers in a mating fiber optic connector.
As communications networks are required that will support higher and higher data rates, there is a demand for fiber optic cables that will support these higher data rates. One way that has been proposed for meeting the demand for increased communications bandwidth is the deployment of fiber optical cables that use “multi-core” optical fibers. A multi-core optical fiber refers to an optical fiber that includes more than one core that is used for transmission of optical communications signals. FIG. 2 is a cross-sectional view of a typical multi-core optical fiber 50. As shown in FIG. 2, the multi-core optical fiber 50 includes a central core 60 and a plurality of satellite cores 61-66. The central core 60 may have the same diameter as the satellite cores 61-66 or may have a different (e.g., larger) diameter. A cladding 70 surrounds the central core 60 and the satellite cores 61-66. The cladding 70 has a lower index of refraction than the central core 60 and the satellite cores 61-66. A buffer coating 80 protects the cores 60-66 and the cladding 70 from moisture and/or physical damage. As a multi-core optical fiber has a plurality of cores, each of which serves as a separate transmission medium, a multi-core optical fiber may have significantly increased transmission capacity as compared to a traditional “single-core” optical fiber. A multi-core optical fiber is known in the existing art. See for example, U.S. Pat. Nos. 5,734,773 and 6,154,594 and U.S. Published Applications 2011/0229085, 2011/0229086 and 2011/0274398, each of which is herein incorporated by reference.